Gloworm combi boiler loosing pressure (CX30)

[Rostyle]

Hi all, after searching on this site and attempting to find the reason for pressure loss on the heating system I carried out the following..
Fistly a visual inspection of all pipes and radiators, valves etc.... No evidence of water leaks ( nearly all pipes are surface mounted and above floor level.)

So I turned my attention to the boiler as I've managed over the years to do some minor repairs etc

I noticed that the pressure, once topped up to about 1 bar, would then creep up once the boiler was running, then eventually drop back down and eventually after a few days would loose enough pressure to stop working.
I hung a plastic bag over the pressure relief pipe outside and it collected a fair amount of water.
Next I released the Schrader valve on the expansion vessel and water started to escape from it.

So I hope its the expansion vessel that has failed as I understand there's a membrane inside thatch split and let the water past..?

As this is not Gas or electrical affected , I am confident I can replace them myself.

My Only issue is repressurising the expansion vessel. I have seen on the spec sheet it's set at 0.5 bar.... Is this pumped up to pressure before or after the system is refilled via the filling loop.?

Also for the small cost I have opted to change the PRV at the same time..

Thanks for reading this far...! looking forward to the responses..

 

[terryplumb]

Try re charging the EV / pumping it's pressure up. To do so ,you need to release system pressure. Open ,and leave open a drain cock whilst pumping up the EV.

 

[Rostyle]

Thanks I will give that a go tomorrow.

 

[Rostyle]

Quick update… I tried recharging the vessel but it was again erratic holding pressure and dropped off overnight..
So took the plunge and ordered a new vessel… not too hard to replace once I finally drained all the water from the boiler..!
The new vessel appeared to come pre charged at 0.5 bar so topped the water pressure back up, bled all rads although there was no air in any of them and fired the boiler up.

It’s now been 4 days and the pressure is holding steady and the boiler seems to be working better than ever!